Conversion formulas
- L/100 km = 235.215 ÷ MPG (US) = 282.481 ÷ MPG (UK)
- MPG (UK) = MPG (US) × 1.20095
- km/L = 100 ÷ (L/100 km) = MPG (US) × 0.425144
The constants come from exact definitions: 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, 1 imperial gallon = 4.54609 L.
Worked example
A car rated 50 MPG in the UK: 282.481 ÷ 50 = 5.65 L/100 km, which is 50 ÷ 1.20095 = 41.6 US MPG and 17.7 km/L.
MPG conversion table
| MPG (US) | MPG (UK) | L/100 km | km/L |
|---|---|---|---|
| 10 | 12.0 | 23.52 | 4.25 |
| 15 | 18.0 | 15.68 | 6.38 |
| 20 | 24.0 | 11.76 | 8.50 |
| 25 | 30.0 | 9.41 | 10.63 |
| 30 | 36.0 | 7.84 | 12.75 |
| 35 | 42.0 | 6.72 | 14.88 |
| 40 | 48.0 | 5.88 | 17.01 |
| 45 | 54.0 | 5.23 | 19.13 |
| 50 | 60.0 | 4.70 | 21.26 |
| 60 | 72.1 | 3.92 | 25.51 |
Frequently asked questions
How do I convert MPG to L/100 km?
Divide 235.21 by the US MPG figure, or 282.48 by the UK MPG figure. For example 30 US MPG = 235.21 ÷ 30 = 7.84 L/100 km.
Why are lower L/100 km numbers better?
L/100 km measures fuel used for a fixed distance, so a smaller number means less fuel. MPG and km/L measure distance per unit of fuel, so bigger is better.
How do I convert US MPG to UK MPG?
Multiply by 1.20095, the ratio of the imperial gallon (4.54609 L) to the US gallon (3.785411784 L). 30 US MPG is 36.0 UK MPG.
Which unit shows real savings more clearly?
L/100 km (or gallons per 100 miles). Going from 10 to 12 MPG saves more fuel than going from 40 to 50 MPG over the same distance, which MPG figures hide but L/100 km makes obvious.